Process and apparatus for controlling the movements of an injection mold and a handling device

ABSTRACT

In order to control the opening and closing movement of an injection mold (1, 3) and the feed and extraction movement of a handling device (7) for the removal of the molding in a manner which is optimally concerted with no delay, the opening movement of the mold and/or the extraction movement of the handling device is detected in relation to position and speed; if the speed lies in a reference range, a release signal is generated which triggers the feed movement of the gripping device or the closing movement of the mold.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a process and apparatus for controlling themovement of an injection mold and a handling device.

Injection molding machines and similar apparatuses for molding moldedparts from plastic or from other materials are frequently operated inconnection with a handling device, robot, manipulator or the like. Thehandling device or the like has a gripping tool, which can be extendedin between the mold halves of the opened mold and withdrawn again, inorder to remove the molded part from the mold. The opening and closingmovements of the mold and the extending and withdrawing movements of thegripping tool must be carefully coordinated with one another in orderthat collisions and damage are reliably avoided even in cases ofmalfunctioning, but on the other hand no unnecessary time losses occur.

"Patent Abstracts of Japan", Volume 11, No. 315, M 631, discloses acontrol system for the gripping tool of an injection molding machine, inwhich the position of the movable injection mold is continuously sensedand used as a manipulated variable in a control loop controlling theposition of the gripping tool. In an additional control loop, whichcontrols the speed of the gripping tool, the positional deviations ofthe gripping tool and the reference speed of the movable mold serve asmanipulated variables. This control apparatus is elaborate, since it isdependent on a constant position and speed sensing of the movable moldand a speed-controlled drive for the gripping tool. JP-A-62-273816(Patent Abstracts of Japan, volume 12, No. 152, M 695) discloses aninjection molding machine of which the gripping tool carries out alifting and extending movement perpendicularly to the mold-openingmovement and subsequently carries out a co-movement with the openingmold half. The lifting and extending movement commence simultaneously intime with the commencement of the opening of the mold, the co-travelingmovement is controlled in dependence on the opening speed of the mold.This control apparatus is also complicated and elaborate, since itrequires a gripping tool which can move in three spatial directions anda speed-controllable drive for the co-traveling movement of the grippingtool. If it were wished to apply the principle of these known controlsystems also to the withdrawing movement of the gripping tool and theclosing movement of the mold, even more complicated means would berequired for the constant speed control of the closing drive of theinjection mold.

It is known to avoid collisions between tools moved at essentiallyconstant, and mutually independent speed, such as for example moldingtool and gripping tool, by arranging in each case in the travel of themolding tool and the gripping tool a position transmitter whichgenerates a release signal when the tool concerned has, in its openingor withdrawing movement, reached a position at which the extending orclosing movement of the other tool can be safely commenced and completedat a predetermined speed. The position at which the release signal isgenerated need not be the end position, for example of the openingstroke of the molding tool, but it must be ensured that, when generatingthe release signal, the molding tool has already covered part of itsopening travel and has reached such a position that even if the moldingtool jams in this position owing to a malfunction, the gripper cancomplete its extending movement, triggered by the release signal,without risk of damage. Analogously, the gripping tool emits a releasesignal for closing the molding tool when it withdraws from the region ofthe molding tool. This signaling point must also be set in such a waythat, in the event of slow travel or a standstill of the gripping tool,damage during closing of the molding tool is ruled out in this position.

By virtue of these safety measures, the movement of the one tool canalways be released position-dependently only when the other tool hasalready covered a considerable part of its movement stroke. Added tothis is that both the generation of the release signal and the movementtriggered by this in each case takes place with an unavoidable delay,which is caused by the response times of the position sensors, theswitching times of the switching elements responding to the positionsignals and the operating times of the electric, hydraulic or pneumaticfinal control elements to be driven. These add up to produceconsiderable time losses, which are at the expense of the cycle rate ofthe injection molding machine or the like.

The invention is based on the object of designing a process and anapparatus of the specified type in such a way that the movementoperations can be carried out with lower non-productive times and in amore favorable time overlap, without thereby increasing the risk ofdamage in the case of malfunction.

The object of the invention is achieved by providing a process forcontrolling the relative movement of a molding tool and a gripping toolof a molding machine. The molding tool is movable between a closedposition for molding a material and a fully open position. The grippingtool is used to remove a molded workpiece for the molding tool, and ismovable between an extended position in which a portion of the grippingtool is within the molding tool when the molding tool is not closed, anda withdrawn position. The process comprises the steps of determining thespeed of movement of one of the molding tool and the gripping tool at anintermediate position, determining whether the speed of the one of themolding tool and the gripping tool falls within a predeterminedreference range, and, if the speed falls within the reference range,generating a release signal for movement of the other of the moldingtool and the gripping tool, and controlling the movement of the other ofthe molding tool and the gripping tool based upon the release signal.

Another aspect of the invention is a molding apparatus having a moldingtool and a gripping tool. The molding tool moves between a closedposition for molding the material and a fully open position. Thegripping tool is used to remove a molded workpiece from the moldingtool. The gripping tool moves between an extended position in which aportion of the gripping tool is within the molding tool when the moldingtool is not closed, and a withdrawn position. the apparatus alsoincludes signal generation means for generating a signal indicative ofthe position of one of the molding tool and gripping tool as a releasesignal for movement of the other of the molding tool and gripping tool.Furthermore, the apparatus includes control means for controlling theposition of the other of the molding tool and the gripping tool. Thesignal generation means has speed measurement means including means fordetermining the movement speed of one of the molding tool and thegripping tool at an intermediate position before generating the releasesignal, and evaluation means to generate the release signal only if themovement speed falls within a predetermined reference range.

According to the invention, not only the position but in addition thespeed of the moved tool is used as a criterion for generating therelease signal for the other tool. The release signal is generated onlyif, on passing through the signaling position, the moved tool has aspeed corresponding to proper operation. At too low--or possibly eventoo high--speed, operation is malfunctioned, and the generation of therelease signal for the other tool does not occur. This makes it possibleto generate the release signal at an earlier point in time of themovement stroke of the tool than was previously possible, in particularalready at a position in which the tool has not yet completely clearedthe path of movement of the other tool. Establishing that the tool haspassed through this position at the proper speed offers adequatecertainty that the tool will also properly cover the remaining part ofits movement stroke and, as a result, clear the path of movement of theother tool in good time.

In a further refinement of the invention, a repeated or continuousmonitoring of the positions and speeds of the two tools can also takeplace, and it can be established by computational extrapolation whetherthe two movements will proceed without collision. If there is the riskof collision, the computer can control a corresponding influence on oneor both movements, ie. termination, braking or acceleration.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention is explained with reference to thedrawings, in which:

FIGS. 1-3 diagrammatically show a molding tool of an injection moldingmachine and a gripping tool of a handling device in various relativepositions with respect to each other;

FIG. 4 shows time-travel diagrams of the two tools;

FIG. 5 shows another time-travel diagram of the two tools to illustratethe collision monitoring.

DETAILED DESCRIPTION OF THE INVENTION

The invention is explained below with reference to an injection moldingapparatus for plastics, but can in principle be applied in the case ofany molding machines having a gripping tool to be moved between themolding tools.

According to FIG. 1, an injection mold comprises two mold halves ormolding tools 1 and 3, which in the closed position shown enclose a moldcavity 5 for producing a molded part, for example in the form of ahollow article. At least the molding tool 3 is movable and, for openingthe mold, can be displaced by means of drive means (not shown) into theopen position 3' indicated by dot-dashed lines. Any desired referencepoint P of the molding tool 3 in this case covers the path from thestarting position S₀ to the end position S_(end), or during the closingstroke covers the reverse path from S_(end) to S₀. When the mold isopen, a gripping tool 7, which belongs to a handling device, robot,manipulator or the like (not shown), can be extended between the moldingtools 1, 3 in order to grasp the molded part, which is pushed out of themolding tool 3, for example by means of ejectors, and pass it on forfurther treatment.

As shown in FIG. 2, the gripping tool 7 must not be extended until themold half 3 has reached not its end position S_(end) admittedly, but anintermediate position in which the extending travel for the grippingtool 7 is cleared. This position is indicated in FIG. 2 by S_(clear). Inthe case of the process customary until now, the drive for extending thegripping tool is not started until the molding tool 3 has reached theposition S_(clear) and in this position a starting signal for thegripping tool 7 is generated.

According to the invention, however, the position of the movable moldingtool 3 is sensed not at as late a stage as the position S_(clear) butalready at two positions before this, which are diagrammaticallyindicated in FIG. 2 at S₁ and S₂. These positions S₁, S₂ are assignedsuitable signal transmitters 9, 11, by which the positions S₁ and S₂ ofthe movable molding tool 3 are sensed. These sensors are of any type andfamiliar to be a person skilled in the art, for example they may bemechanically actuated electric switches, contactless switches, lightbarriers, digital position pickups or the like. Sensing the positions S₁and S₂ can also take place by means which are assigned to the pneumaticor hydraulic drive system for the molding tool.

The two sensors 9, 11 are connected to an evaluation device 13, in whichthe time interval Δt which lies between the signals generated by thesensors 9 and 11 can be sensed. This time interval Δt, in which themolding tool 3 covers the path from S₁ to S₂, is a measure of the speedof the molding tool on passing through the position S₂. This timeinterval Δt is compared with predetermined limits of a reference valuerange, and in an output line 13 a release signal is generated at thepoint in time at which the molding tool 3 passes through the positionS₂, but only on condition that the measured time interval Δt, andconsequently the speed of the molding tool 3, lies in the predeterminedreference range. The commencement of the extending movement of thegripping tool 7 is triggered by the release signal.

As indicated in FIG. 2, it is possible by the process according to theinvention to generate the release signal already at the position S₂ ofthe molding tool 3, although at this point in time the molding tool 3has not yet completely cleared the extending travel for the grippingtool 7, ie. has not yet reached the position S_(clear). If, owing to amalfunction, the molding tool were to come to a standstill in theposition S₂, damage to the gripping tool 7 would be the consequence.However, measuring the time interval Δt provides the guarantee that therelease signal is generated in the position S₂ only if the molding tool3 moves at a speed corresponding to normal operation. It can then beassumed, if only for reason of the mass inertia, that the molding tool 3will still cover at least the travel path from S₂ to S_(clear) even inthe event of a malfunction, so that damage cannot occur during extendingof the gripping tool 7.

FIG. 3 illustrates how, in an analogous way, in the case of thewithdrawal stroke of the gripping tool 7 the release signal is generatedfor the closing movement of the molding tool 3. The gripping tool 7moves out of the completely extended position P_(ext) into thecompletely withdrawn position P_(withd) and thereby runs through aposition P_(clear), in which the closing travel for the molding tool 3is completely cleared so that the molding tool 3 can be moved safelyinto the closed position (FIG. 1). According to the prior art, astarting signal for the closing movement of the molding tool 3 is notgenerated until the gripping tool 7 has reached the position P_(clear).According to the invention, however, two positions P₃ and P₄ of thegripping tool 7 are sensed by means of suitable sensors (not shown inFIG. 3) already before reaching the position P_(clear), and from thesignals of the sensors the time interval Δt in which the gripping tool 7covers the path from P₃ to P₄ is determined. If this interval Δt, andconsequently the speed of the gripping tool 7, lies in the referencevalue range characteristic for normal operation, a release signal forthe commencement of the closing movement of the molding tool 3 can begenerated already in the position P₄ of the gripping device 7. Theproper speed of the gripping tool 7, established at the point P₄, offersthe guarantee that the gripping tool will also cover the remainingtravel up to at least the position P_(clear) and not hinder the closingmovement of the molding tool 3.

FIG. 4 diagrammatically shows time-travel diagrams, the curve A beingintended to reproduce the opening and closing stroke of the molding tool3 and the curve B being intended to reproduce the extending andwithdrawing stoke of the gripping tool 7. At the point in time t₀, themolding tool 3 commences its opening stroke up to the end positionS_(end) and thereby passes through the positions S₁ and S₂ sensed bysensors at the points in time t₁ and t₂. The time interval Δt₁ betweenthe points in time t₁ and t₂ is sensed and compared with referencevalues. If the time interval lies in the reference value range, anrelease signal for the start of the movement of the gripping tool 7 isessentially generated at the point in time t₂. For triggering themovement of the gripping tool, an unavoidable, constant switching timeΔt₀ is required, so that the extending movement of the gripping tool 7is started at a point in time t'₂. This point in time t' ₂ may, however,lie distinctly before the point in time t_(f), at which the molding tool(curve A) passes through the position S_(clear) (see FIG. 2), in whichit no longer hinders the extending of the gripping tool.

In the withdrawal stroke of the gripping tool 7, which commences at thepoint in time t_(x), the gripping tool passes through the positions P₃and P₄ sensed by means of sensors, and, dependent on the time intervalΔt₄ elapsed in between, at the point in time t₄ a release signal isgenerated, which in turn after a corresponding switching time Δt₀, atthe point in time t'₄, controls the commencement of the closing strokeof the molding tool 3. This point in time t'₄ also lies before the pointin time t_(y), at which the gripping tool 7 in the position P_(clear)(see FIG. 3) has fully cleared the path of movement of the molding tool3. It can be appreciated that the invention permits a very favorabletime overlap and optimum mutual adaptation of the movement operations,without sacrificing operational reliability.

Modifications of the embodiment described are possible within the scopeof the invention. For instance, the position and speed sensing can takeplace in a way other than that described. For example, instead of fixedposition signal transmitters, a position detector arranged on themovable part, such as mold half 3 or gripping tool 7, may be used, whichposition detector detects or scans two or more fixedly arranged travelmarkers, or else possibly a continuous sequence of travel increments.Instead of a measurement of the time interval between two positions, adirect speed measurement may also be performed by corresponding speedsensors. Consequently, for example one of the two position transmitters9, 11 in FIG. 2 may be omitted and the other position transmitterassigned an additional speed sensor.

In a further refinement of the invention, a continuous position andspeed monitoring of the two tools can take place during their entiremovement. At any desired intermediate positions which one of the toolsreaches, it can be inquired whether what is respectively the other toolhas reached the position and speed required for the proper movementsequence. For explanation, reference is made to FIG. 5. Here, like inFIG. 4, the time-travel diagram is shown for the opening movement of themold (curve A) and for the extending movement of the gripping tool(curve B), these movements, which in reality proceed at right angles toeach other, being shown here oppositely directed in order to illustratethe possibility of collision.

According to FIG. 5, at the point in time t₀, the molding tool commencesits opening stroke until in the end position S_(end) and during thispasses at point in time t_(f) through the clearance position S_(clear),from which it can no longer hinder the extending movement of thegripping tool. The travel path from S₀ to S_(clear) is the collisionregion. As long as the molding tool is still in this region, collisionswith the extending gripping tool are possible. At the position S₂ at thepoint in time t₂, a position and speed measurement of the moved moldingtool is carried out and, dependent on the measuring result, the releasesignal for the extending movement of the gripping tool is triggeredafter a time delay Δ_(t) at the point in time t₂ '. Said gripping toolthen moves out of the withdrawn position P_(withd) into the fullyextended position P_(ext) and passes at the point in time t_(k) throughthe position P_(clear), at which the region of possible collisions withthe molding tool begins. Since the molding tool has already left thecollision region beforehand at the point in time t_(f), a collision doesnot occur. According to the invention, the triggering point in time t₂ 'for the extending movement of the gripping tool can be chosen such thatthe point in time t_(k) lies after the point in time t_(f) withcertainty but as little after as possible.

In reality, the movements cannot be fixed exactly in time but have arange of tolerance, which is indicated in FIG. 5 by the dashed straightlines A' for the molding tool and B' for the gripping tool. Due todeviations in this range of tolerance, the points in time t_(f) andt_(k) may be shifted, for example to t_(f) ' and t_(k) ', so that thegripping tool can collide with the molding tool. In order to rule thisout with certainty, the point in time t₂ ' at which the extendingmovement of the gripping tool is triggered could be retardedappropriately, as a result of which however the advantage achieved bythe invention would be partially lost again. In order to be able tooperate with as early a triggering as possible of the extending movementof the gripping tool, ie. with greatest possible time overlap of the twomovements, according to one embodiment of the invention it is envisagedto measure the position and speed, at least of the molding tool, onceagain at at least one further point in time t₃. It is particularlyadvantageous if this measurement is triggered when the gripping tool hasreached an intermediate position P₃ which can be sensed by positionpickups. This means in other words that, on passing through the positionP₃, the gripping tool "inquires" the position and speed of the moldingtool at the point in time t₃. This may be repeated at further points intime, or else take place continuously during the entire movement ofmolding tool and gripping tool before reaching the position P_(clear).The inquired measured values are then fed to a computer, which on thebasis of the sensed positions and speeds extrapolates the movements ofthe molding tool and gripping tool and establishes whether a collisionis avoided with adequate certainty or whether signals generated by meansof the computer have to be used to intervene in the control of the twomovements.

I claim:
 1. A process for controlling the relative movement of a moldingtool and a gripping tool of a molding machine, the molding tool beingmoveable between a closed position for molding a material and a fullyopen position, the gripping tool being used to remove a molded workpiecefrom the molding tool and being movable between an extended position inwhich a portion of the gripping tool is within the molding tool when themolding tool is not closed and a withdrawn position, the methodcomprising:determining the speed of movement of one of the molding tooland the gripping tool at at least one intermediate position, determiningwhether the speed of the one of the molding tool and the gripping toolfalls within a predetermined reference range, and if the speed of theone of the molding tool and the gripping tool falls within thepredetermined reference range, generating a release signal for movementof the other of the molded tool and the gripping tool, and controllingthe movement of the other of the molding tool and the gripping toolbased upon the release signal.
 2. The process as claimed in claim 1,wherein the release signal is generated before the point in time atwhich the one of the molding tool and the gripping tool has reached aposition at which it can no longer hinder the movement of the other ofthe molding tool and the gripping tool.
 3. The process as claimed inclaim 1, wherein a further speed measurement takes place at at least onefurther intermediate position of the one of the molding tool and thegripping tool, and wherein a control signal for influencing the movementof the other of the molding tool and the gripping tool is triggered ifthe measured speed does not lie in a reference range.
 4. The process asclaimed in claim 3, wherein the further speed measurement is initiatedwhen the other of the molding tool and the gripping tool has reached apredetermined intermediate position of its movement.
 5. The process asclaimed in claim 1, wherein the speed and position of each of themolding tool and the gripping tool is continuously monitored, and themeasured values of speed and position are fed to a computer in order toestablish, by computational extrapolation, whether movement of themolding tool and gripping tool will proceed without collision, andwherein, if this is not the case, a control signal for influencing themovement of one of the molding tool and the gripping tool is generated.6. A molding apparatus, including a molding tool which moves between aclosed position for molding a material and a fully open position, agripping tool for removing a molded workpiece from the molding tool, thgripping tool moving between an extended position in which a portion ofthe gripping tool is within the molding tool when the molding tool isnot closed and a withdrawn position, signal generation means forgenerating a signal indicative of the position of one of the moldingtool and gripping tool as a release signal for movement of the other ofthe molding tool and gripping tool, and control means for controllingthe position of the other of the molding tool and the gripping tool, thesignal generation means having speed measurement means including meansfor determining the movement speed of the one of the molding tool andthe gripping tool at at least one intermediate position beforegenerating the release signal, and evaluation means to generate therelease signal only if the movement speed falls within a predeterminedreference range.
 7. The apparatus as claimed in claim 6, wherein thespeed measurement means further includes means for measuring the speedof each of the molding tool and gripping tool at a plurality oflocations.
 8. The apparatus as claimed in claim 7, wherein measurementof the speed of each of the molding tool and the gripping tool istriggered by a signal generated by the other of the molding tool and thegripping tool.
 9. The apparatus as claimed in claim 7, wherein the speedmeasurement means is a computer with prevents collisions of the moldingtool and gripping tool.